Rapid prototyping, additive manufacturing, or 3D printing processes utilize a three-dimensional (3D) CAD file to produce a 3D object. Numerous methodologies have been described in prior art, the most common including selective-laser-sintering (“SLS”), stereolithography (“SLA”), inkjet printing, and extrusion based 3D printing or FFF (fused filament fabrication).
Several types of low temperature thermoplastic polymers, such as ABS (acrylonitrile butadiene styrene) and PLA (polylactic acid) are used in additive manufacturing for prototyping. Higher-end engineering polymers, such as polyetheretherketone (PEEK), polyetherketoneketone (PEKK), polyphenylsulphone (PPSU), polycarbonate (PC), and polyetherimide (PEI) are used for fixtures or higher temperature applications. Fiber fillers, such as carbon, or glass fibers, have been added to polymers used for additive manufacturing to enhance the mechanical properties. Although the stiffness increases with increased fiber loading as expected, the tensile strength does not increase proportionally with the fiber loading for 3D printed parts. Testing of these 3D printed parts have demonstrated that the tensile strength for these parts are around 40% to 60% less than the tensile strength of the same parts made through injection molding or machining.
Using a specific example involving Fused Filament Fabrication, carbon fiber and glass fiber polymer filaments have a rough, uneven surface. As the fiber loading increases, the surface roughness and unevenness in filament diameter also increases. The surface roughness and aberrations result in a brittle filament, which is difficult to handle and process in a 3D printer. Moreover, filament with surface variations can cause the motor and incoming filament to stall, resulting in voids or gaps in the printed part/objects. The nozzle extrudate, material exiting the printing nozzle, also shares the same surface roughness and brittle nature of the feed filament. The extrudate boundaries created during the printing of a 3D object are the mechanically weak areas of the part. Thus, under loading, the 3D printed parts fail at these boundaries through crack propagation, delamination, or another failure mode. For achieving the best possible material properties for Fused Filament Fabrication, the polymer filament and resulting nozzle extrudate must have a uniform and smooth surface.
Therefore, there exists a need to improve the material properties of fiber filled polymer materials used for additive manufacturing.
Furthermore, there exists a need to achieve a smoother and uniform surface finish for the printing material (and nozzle extrudate for Fused Filament Fabrication) to enhance the material properties and improve the ease of handling.